The present disclosure generally relates to a flexible manufacturing system for vehicle assembly, and more particularly, to a magnetorheological reconfigurable clamp for providing support for a variety of different body panel configurations employed in the vehicle assembly without requiring manual adjustment or reprogramming.
The advent of assembly lines has enabled rapid, mass production of products at a reduced product cost. Assembly lines typically include multiple operation stages with component, material or sub-assembly inputs. Sometimes the workpieces are similar or related part shapes. Other times, the workpieces are of unrelated design but require similar manufacturing operations. In these varied applications, the fixture reconfiguration or changeover from one part design to another has to be fast enough to meet the productivity requirements of current manufacturing systems.
Previous efforts in designing and developing flexible fixturing for either small batch manufacture or mass production scenarios can generally include the use of modular fixtures and conformable fixtures. Modular fixturing generally includes fixtures assembled from a standard library of elements such as V-blocks, toggle clamps, locating blocks, and the like. Their flexibility lies in the ability to be reconfigured either manually or by a robotic device. However, modular fixtures have no intrinsic ability to adapt to different sizes and shapes of parts within a part family. In addition, the time necessary for reconfiguration is long and modular fixtures generally lack stiffness. As a result, modular fixtures are more suited to a job shop environment rather than mass production.
The advent of Flexible Manufacturing Systems (FMS) in the early 1960's provided the impetus for work on conformable fixturing. A conformable fixture is defined as one that can be configured to accept parts of varying shape and size. Conformable fixture technology generally includes encapsulant or mechanistic techniques. Examples of encapsulant fixtures are found in the aerospace industry, where low melting-point metals are used to enclose turbine blades and produce well-defined surfaces for part location and clamping for grinding operations. While an excellent means of facilitating the holding of complex parts, encapsulation is a costly and time-consuming process.
Mechanistic fixtures reported in the literature include the use of petal collets, programmable conformable clamps, a programmable/multi-leaf vise, an adjustable integral fixture pallet, and the like. Of these, the adjustable integral fixture pallet concept appears to be the most capable of accommodating a part family of castings. To date, however no feasibility studies have been conducted regarding the applicability of any of these techniques to production machining operations.
One troublesome area in flexible manufacturing systems is its implementation in body shops. Clamps are typically employed to support the various sheet metal workpieces, e.g., body panels, during assembly and clamping can potentially scratch the exposed surface and/or locally deform the workpiece, affecting its aesthetic quality. While, ideally, clamping could be performed on flanges or surfaces that are invisible or immaterial to end users, some clamping inevitably occurs on exposed surfaces.
Current clamps utilized in assembly lines generally include a clamp block, which accurately matches the contours of the workpiece and a matching pressure foot. In operation, the clamp block supports the exterior surface of the workpiece while the pressure foot contacts the inner (non-exposed) surface with a compliant pad shaped to approximate, in the unloaded condition, a point. With this approach, minor differences between the shape of the workpiece and the clamp block geometry can be accommodated without introducing local deformation. As a result, the contour of each clamp block is generally specific to a limited number of work pieces and surfaces. In dedicated facilities, the contours of the clamp block are generally fabricated by numerically controlled (NC) machining using data generated from the workpiece to be fixtured. A problem arises if multiple models are produced having significantly different workpiece configurations. Multiple clamp blocks having different contours are then required to accommodate the multiplicity of workpiece configurations.
Accordingly, there remains a need for a reconfigurable clamp block that can provide adequate support for a variety of workpiece configurations.